Audio Test: It's All About Mobile Devices

We seem to have audio equipment all around us -– TVs, home entertainment systems, radios, computers, phones, tablets, and, yes, stereo systems all have speakers. Sound is ultimately a change in air pressure, but it travels in electrical form over analog cables, digital cables, and digital wireless connections.

Testing takes place in amplifiers, codecs, digital transmitters, and speaker drivers. To find out what's going on in audio testing, I spoke with Tom Kite, vice president of engineering at Audio Precision, by telephone.

Martin Rowe: With all of our portable devices having speakers and microphones, have mobile devices become a significant part of audio testing?

Tom Kite: Everything seems to have an integrated speaker these days. When we plan new products, we no longer think exclusively about audio-visual receivers with many inputs and outputs. AV receivers keep getting loaded with more and more I/O, but the audio world is moving to mobile devices. Everything needs to connect easily to a mobile device. Audio receivers seem to be giving way to sound bars. Today you beam your audio to your sound bar from your phone. It's the mobile device manufacturers that seem to have the budgets for audio testers these days. We're also seeing new chips coming out that handle audio. It's still a young market.

Martin Rowe: I have a stereo, and I never listen to it. All my music is either contained or controlled by a mobile device. Has audio quality improved in mobile devices?

Tom Kite: Some people complain about audio quality on mobile devices, especially when streamed over Bluetooth, but it's all about being mobile now. People want the convenience of having mobile audio, but they're used to good audio quality. Bluetooth can provide good quality audio, because codecs have improved.

Martin Rowe: Despite all the digital connectivity in audio devices, sound is still sound. How is audio test performed on today's devices, given all the digital connectivity used today?

Tom Kite: We noticed that our customers started asking to use AP's audio test equipment for acoustical analysis in addition to decoding digitized audio on mobile devices. We already had the hardware and measurements for that, but just needed more measurements to round out the electroacoustic testing. More and more devices have both electronics and transducers today. TVs and cellphones have finely tuned electronics to compensate for deficiencies in their driver, producing a better sound.

Because there are so many different forms that audio can travel –- analog, SP/DIF, Bluetooth, HDMI, etc. -- we've developed modular test equipment. You might test an amplifier by direct connections, or you can analyze digitized audio to test codecs. For testing drivers, you might test them when they come in from the supplier, but you'll likely test again once assembled into the final product as a complete system.

Martin Rowe: How do you test drivers?

Tom Kite: Makers of Bluetooth audio products want to test their devices with a known quality analog audio signal, send it over Bluetooth, and measure audio quality coming out of the driver. They also want to measure the audio quality along the entire chain -- analog and digital. Acoustical measurements are made with microphones. We are a technology partner with GRAS Sound and Vibration, and we use their microphones. They plug into the analog inputs of our test equipment.

Many of our customers like having one piece of test equipment for everything. That's why we developed modular audio testers that can test analog, digital, and acoustic signals. For testing speakers, we can measure the impedance of a speaker driver and its acoustical outputs. Frequency response is an important test, but we can also measure rubs and buzz that cause unwanted noises.

Martin Rowe: What is rub-and-buzz testing, and what does it tell you?

Tom Kite: Rub and buzz is an acoustical measurement. You have two ways to tell if a driver meets its spec before it rolls off the product line.

There are different ways to approach rub and buzz. You can look at crest factor, higher-order harmonics, or both. Comparing rub-and-buzz testing with frequency response measurements lets you see a driver's performance differently, but there are correlations between them. For example, undetectable rub and buzz -- the ear may not hear it, but the equipment does. What do you do? Some companies look at that and figure that it might cause an unwanted failure later in time, and that should be addressed. Other manufacturers say, if it sounds good now, ship it. Some people say they should use psycho-acoustical analysis and decide whether or not to ship a driver. We can provide the data, but it's up to the manufacturer to decide what to do with it.

@David, that's why I keep POTS phones and dont go to VoIP with Comcast, no matter how many times the call trying to get me to sign up. My office phone is a voice phone running on my DSL service. At frst, it was unusable after a few minutes. the voice would break up. Changing modems has solved the problem.

@MB I would wholeheartedly agree with you. The silly thing is that POTS phones are still limited to around 3 to 4 KHz by the codecs, and they still sound great. We recently swapped our good old TDM PABXs at work for a VOIP system. It's good when it works, but we've had no end of niggly problems. And guess what? If your network connection is bad or down you have NO Comms at all! No email, no phones, no IM, NOTHING! Come back TDM/ISDN, all is forgiven!

My nephew tried to connect using hiw Windows 8 computer and said it wouldn't connect. Itried with my Win7 and it found the devices but asked for drivers. I downloaded the drivers but because UBM won;t give me admin rights, I was unable to install. We have a fairly new Android tablet here and a phone so I'll try them.

I wonder if the BT-only-compatible-with-Apple is still true. This seems like it might be a leftover from the days when Android didn't support BT 4.0 (BT Low Energy). Those days were not that long ago, and millions of consumers are still using Android phones that don't support this.

Today, I joined the crowd and bought a JBL Charge bluetooth speaker, a step up from the one shown above. It works fine with Apple devices and in fact, the box indicates that it's only Bluetooth compatible with Apple. Some of the reviews on Amazon point to that incompatibility fact; buyers didn't know that when they bought theirs.

@JeffL_2 thanks so much for explaining that horrible sound that comes out of the phone when I'm on hold. Since so many of us spend so much time on hold, I'd think that the "on hold Muzak people" would select material that can tolerate the low bandwidth or provide some peaceful silence (with periodic confirmations that the line is alive).

I'm not surprised that test equipment exists to measure this but I'm more than a little surprised that there's real popular concern. So many of these modern mobile links just "assume" that the traffic over a link is almost exclusively voice that these links automatically route all traffic through a vocoder path in order to reduce the data rate of the traffic. If you've ever waited on a cell phone for a long time for service (like for support for a federal or state program like benefits) you've noticed the absolutely abysmal quality of "music on hold", it sounds almost literally (to recycle a very old quote) "as if someone pushed the RCA pooch into the horn" (yes it was a joke on their old "his master's voice" logo). You get that hideous sound because the link is trying to "vocode" music (possibly an entire symphony orchestra) and pass it over a link at a few thousands bits per second! My goodness if people are willing to tolerate THAT annoying abuse (and you seldom hear anyone bring it up, although it happens literally all the time) it makes me wonder what the heck WOULD they be prepared to complain about??

@DrQuine. Audio test of speakers and amplifiers in phones assumes a good quality signal. I think that the audio testing os more for music than telephone voice. Unfortunately, even a good quality audio subsystem is at the mercy of the cellular network. At this point, I think telephone service is assumed; the carriers and cell phone makers are more interested in the audio quality of music, movies, and games.